As is known, public telephones, especially telephones installed in call boxes which provide shelter, have for a long time proved to be a focus of attention for deliquents, and therefore in this type of telephone more and more resistant bodies have been used, keyboards which are more robust and in general it has been the intention to make the apparatus more inviolable in all its aspects.
Nevertheless, the remedies which have been adopted in this respect lack "flexibility", since "from them are derived monobloc units in which it is not possible to make modifications, so that each specific application of a defined type of telephone conforms to a practical embodiment substantially different from all the rest, practically throughout the whole of the process of constructing it.
However, in practice sometimes telephones working exclusively with coins are required, sometimes exclusively with credit cards or working indiscriminately with one or the other of the methods of payment, and therefore it would be desirable to have a telephone which, starting with a basic structure which does not change, could be adapted to any one of these requirements.
It would also be desirable to have a rapid and simple form of assembly, in spite of the extraordinary structural rubustness which this type of public telephone should offer, but nevertheless conventional telephones of this type have a complex form of assembly.
Another problem of this type of telephone is centred around certain weak points which exist in them which make them vulnerable, as for example the liquid crystal screen by means of which information is passed to the user, or the exit slot for coins which were not needed or which are defective.
A problem public telephones also suffer from is that it is impossible to keep control over the money collected, so that it depends upon the honesty of the collectors, since although there are means of electronically counting the coins which are inserted in the apparatus, in many cases the theoretical figure cannot coincide with the real figure because of failures in the apparatus or because of the various tricks employed by some users, which do not permit the categorical establishment of whether some coins are missing through theft by the user or by the collector.